OFFSET
1,5
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
Multiplicative with a(p^e) = (p-3)^e. If n = Product p(k)^e(k) then a(n) = Product (p(k)-3)^e(k). a(3k) = 0 for k >= 1. Abs (a(2^k)) = 1 for k >= 1.
Sum_{k=1..n} a(k) ~ c * n^2 / 2, where c = Product_{p prime} (p*(p-1)/(p^2-p+3)) = 0.196347937547... . - Amiram Eldar, Jan 20 2024
MATHEMATICA
a[1] = 1; a[p_?PrimeQ] := p-3; a[n_] := Times @@ Power @@@ ({#[[1]]-3, #[[2]]}& /@ FactorInteger[n]); Array[a, 72] (* Jean-François Alcover, Jul 19 2017 *)
PROG
(PARI) a(n) = my(f=factor(n)); for (i=1, #f~, f[i, 1] -=3); factorback(f); \\ Michel Marcus, Jun 09 2014
CROSSREFS
KEYWORD
sign,easy,mult
AUTHOR
Jaroslav Krizek, Oct 17 2009
EXTENSIONS
More terms from Michel Marcus, Jun 09 2014
STATUS
approved